These are lessons, a lesson spaced phrase.

The thing that I did that most improved my English what was listening to the radio?

The most important thing would improve.

My English is to move here in England.

The thing that most improved my English is probably taking some evening courses.

I think the thing that most improved my English was reading books in English.

It's helped Mark develop my vocabulary tremendously.

The thing that most helped me with my English was marrying on English woman.